The present invention relates to flame resistant fabrics. More particularly, the present invention relates to fabric blends containing inherently flame resistant fibers and flame resistant cellulosic fibers that contain a flame retardant compound. These fabrics exhibit excellent flame resistance, minimal shrinkage when laundered, and can be produced in a full range of colors and shades.
Inherently flame resistant fibers are highly resistant to heat decomposition and are therefore desirable in the manufacture of flame resistant garments intended for environments in which flames or extreme heat will be encountered. These desirable properties of inherently flame resistant fibers can, however, create difficulties during fabric production. For example, fibers composed of aromatic polyamide, commonly known as aramid fibers, are difficult to dye. Aramid fiber suppliers have recommended complicated exhaust dyeing procedures with various dye-assistants, high temperatures, and long dyeing times to effect dyeing of these fibers. Such dyeing conditions require substantial amounts of energy both to maintain the dyeing temperature and for the treatment of waste dyebaths. Dye-assistants comprised of organic agents, and commonly referred to as carriers or swelling agents, are used to enhance dyeability. Such dye-assistants may be added to the dyebath as a treatment prior to dyeing, or can be integrated into the inherently flame resistant fiber during its production.
Inherently flame resistant fibers such as aramid fibers can be blended with fibers made of other materials. As is known in the art, fiber blending can be used to obtain an end fabric that combines the beneficial characteristics of each of the constituent fibers. For instance, in the area of flame resistant fabric manufacture, flame resistant cellulosic fibers such as flame resistant rayon (xe2x80x9cFR rayonxe2x80x9d) fibers can be successfully blended with aramid fibers to obtain a flame resistant material which is softer, more moisture absorbent, and less expensive to produce than materials constructed only of aramid fibers.
Although improving the texture and lowering the cost of flame resistant fabrics, blending inherently flame resistant fibers with flame resistant cellulosics such as FR rayon can complicate production. Specifically, cellulosics contain flame retardant agents that, although resistant to standard cellulosic dyeing procedures, tend to be depleted by the extreme temperatures generally considered necessary to dye the inherently flame resistant fibers. This depletion of flame retardant agents significantly reduces the flame resistance of the cellulosic fibers and therefore reduces the flame resistance of these blends. Moreover, these conditions increase the likelihood of further depletion of the flame retardant agents during subsequent launderings and an even greater reduction in flame resistance.
Due to the danger of depleting the flame retardant agent or agents contained in the cellulosic fibers of such fabric blends, producers of cellulosic fibers often advise their customers to avoid dyeing the inherently flame resistant fibers when blended with flame resistant cellulosic fibers. As an alternative, these producers suggest using producer colored inherently flame resistant fiber where a colored, flame resistant cellulosic blend is desired. In producer coloring (also known as xe2x80x9csolution dyeinxe2x80x9d), pigment or other coloring is typically injected into the polymer solution before the fiber is formed. Although providing for adequate colorization of these fibers, producer coloring presents several disadvantages. First, producer colored fibers usually are more expensive than non-producer colored fibers. Second, due to the increased difficulty and cost associated with the production of these fibers, typically only a limited variety of producer colored fibers are available.
In addition to increasing the difficulty of dyeing the inherently flame resistant fibers, dyeing at temperatures below 100xc2x0 C. renders the inherently flame resistant fibers susceptible to substantial laundry shrinkage. Accordingly, where the inherently flame resistant fibers are to be dyed, the dyer is typically left with a choice between acceptable color and shrinkage control but unacceptable flame resistance on one hand (when dyeing above 100xc2x0 C.), and preserved flame resistance but high laundering shrinkage and poor color yield on the other (when dying below 100xc2x0 C.). Notably, the same shrinkage susceptibility exists in situations where the inherently flame resistant and/or flame resistant cellulosic fibers are not dyed.
From the above discussion, it can be appreciated that it would be desirable to have fabric blends comprising inherently flame resistant fibers and flame resistant cellulosic fibers that avoid the aforementioned problems.
The present disclosure relates to flame resistant fabrics that comprise a plurality of inherently flame resistant fibers and a plurality of cellulosic fibers containing a flame retardant compound. Normally, the flame resistant fibers were uncrystalized in fiber form and the cellulosic fibers contained a flame retardant compound in fiber form.
In one arrangement, the inherently flame resistant fibers comprise a material selected from the group consisting of aromatic polyamide, polyamide imide, polyimide, and mixtures thereof, while the cellulosic fibers comprise a material selected from the group consisting of rayon, acetate, triacetate, lyocell, and mixtures thereof.
In another arrangement, the fabric contains a residual amount of a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.
In a further arrangement, the fabric contains a phosphorus compound flame retardant in a concentration of at least approximately 1.4% phosphorus by weight of cellulosic fiber component.
In yet another arrangement, the fabric exhibits a duration of afterflame no greater than 2.0 seconds when subjected to a vertical flammability test conducted in accordance with FTMS 191A Method 5903.1 using a three second exposure.
In a further arrangement, the fabric exhibits a shrinkage percentage of no greater than approximately 7% after 20 launderings conducted in accordance with AATCC Test Method 135-1992, Table I (3)(V)(A)(iii).
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.